The present application relates to a liquid-crystal display apparatus operating in an FFS (Fringe Field Switching) mode. More particularly, the present application relates to a liquid-crystal display apparatus operating in an FFS mode of a two-domain type in which two slit portions having orientation directions different from each other are joined together to each other.
In comparison with the CRT (Cathode Ray Tube) display apparatus, the liquid-crystal display apparatus has characteristics that the liquid-crystal display apparatus is thin as well as light and consumes little power. Thus, the liquid-crystal display apparatus is used in a number of electronic apparatus as a display unit. In the liquid-crystal display apparatus, liquid-crystal molecules are aligned in a direction determined in advance by carrying out a rubbing process for an oriented film. Then, the direction of each liquid-crystal molecule is changed by an electric field in order to vary light quantities such as the quantity of transmitted light and the quantity of reflected light so as to display an image.
As methods for applying an electric field to a liquid-crystal layer employed in a liquid-crystal display apparatus, there are a vertical electric field method and a horizontal electric field method which are adopted as follows.
In a liquid-crystal display apparatus adopting the vertical electric field method, a pair of electrodes provided to sandwich a liquid-crystal layer apply an electric field oriented in approximately vertical direction to liquid-crystal molecules. As liquid-crystal display apparatus adopting the vertical electric field method, there are liquid-crystal display apparatus such as a liquid-crystal display apparatus operating in a TN (Twisted Nematic) mode, a liquid-crystal display apparatus operating in a VA (Vertical Alignment) mode and a liquid-crystal display apparatus operating in an MVA (Multi-domain Vertical Alignment) mode.
In a liquid-crystal display apparatus adopting the horizontal electric field method, on the other hand, a pair of substrates are provided to sandwich a liquid-crystal layer. A specific side of the liquid-crystal layer is a side close to one of the substrates. On this specific side of the liquid-crystal layer, a pair of electrodes insulated from each other are provided to serve as electrodes for applying an electric field oriented in approximately horizontal direction to liquid-crystal molecules. As liquid-crystal display apparatus adopting the horizontal electric field method, there are liquid-crystal display apparatus such as a liquid-crystal display apparatus operating in an IPS (In-Plane Switching) mode and a liquid-crystal display apparatus operating in an FFS mode. The IPS mode is known as a mode in which the two electrodes are not placed at locations superposed on each other if seen in a planar view. On the other hand, the FFS mode is known as a mode in which the two electrodes are placed at locations superposed on each other if seen in a planar view.
In particular, in the liquid-crystal display apparatus operating in the FFS mode, the two electrodes insulated from each other by an insulation film are upper and lower electrodes provided on different layers. The upper electrode is provided with slit openings. An electric field passing through the slit openings in approximately horizontal direction is applied to liquid-crystal molecules. The liquid-crystal display apparatus operating in the FFS mode has effects that the apparatus is capable of providing a large viewing-field angle and improving the contrast of the image. Thus, the liquid-crystal display apparatus operating in the FFS mode is used in a number of applications in recent years.
As described above, in the liquid-crystal display apparatus operating in the FFS mode, the upper electrode is provided with a plurality of slit openings. If the slit openings are oriented in one inclined direction, that is, if the slit openings are configured to adopt a one-domain type, gaps ranging from the gap between two adjacent slit openings to the gap between the electrodes can each be made constant. Thus, a high aperture ratio and a high transmission factor can be achieved. If the slit openings are oriented in two directions, that is, if the slit openings are configured to adopt a two-domain type, it is possible to provide a large viewing-field angle and improve the contrast of the image. For details, the reader is advised to refer to Japanese Patent Laid-open Nos. 2000-010110 and 2002-182230. If the slit openings are configured to adopt a two-domain type, however, due to portions obtained as a result of orienting the slit openings in the two inclined directions, there are locations at which gaps ranging from the gap between two adjacent slit openings to the gap between the electrodes become large. It is not possible to effectively make use of locations, at which gaps ranging from the gap between two adjacent slit openings to the gap between the electrodes become large, as locations for displaying an image. Thus, the aperture ratio virtually decreases. In order to solve this problem, in a liquid-crystal display apparatus disclosed in Japanese Patent Laid-open No. 2007-264231 as a liquid-crystal display apparatus operating in the FFS mode, the slit openings oriented in directions different from each other are joined to each other in order to reduce the number of edges. By reducing the number of edges, it is possible to convert the configuration of the slit openings into a configuration of the two-domain type and increase the aperture ratio.